1. Field of the Invention
The present invention relates to a method for controlling communication of a radio terminal and the radio terminal preferably used in a radio communication system performs communication in, for example, W-CDMA (Wideband-Code Division Multiple Access) method.
2. Description of the Related Art
W-CDMA is one of the radio communication interfaces defined by IMT-2000 (International Mobile Telecommunications-2000) and is regarded as a typical radio communication method.
The maximum transmission rate of 384 kbps of W-CDMA can realize multimedia access for audio, moving image, data and others.
Further, research and development have been recently made for radio communication methods called HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access) based on the W-CDMA technique.
Comparing with the current W-CDMA, HSDPA is a technique for high-speed downlink packet transmission in the direction from a base station to a UE (User Equipment) and HSUPA is a technique for high-speed uplink packet transmission in the reverse direction. HSDPA and HSUPA have been standardized by 3GPP Release 5 (3rd Generation Partnership Project Release 5), and 3GPP Release 6, respectively.
FIG. 2 shows the concept of W-CDMA communication. As shown in FIG. 2, a radio communication in the W-CDMA method is performed between a radio base station 100 and one or more of UEs 200.
In the uplink, DPDCH (Dedicated Physical Data Channel) for transmission of user information, DPCCH (Dedicated Physical Control Channel) for transmission of control information are mapped over the in-phase component (I axis) and the Quadrature component (Q axis) of QPSK (Quadrature Phase Shift Keying) modulation, respectively and are transmitted to the radio base station 100 (see solid arrow A1).
In the downlink, the DPDCH and the DPCCH are time-division-multiplexed and are transmitted to the UE 200 (see broken arrow A2). These downlink channels are dedicated to each UE 200 and transmission through these channels is performed exclusively of the other UEs 200.
Next, FIG. 3 shows the concept of HSDPA communication. As shown in FIG. 3, downlink transmission from the radio base station 100 to the UE 200 is carried out by HSDPA communication.
Specifically, each UE 200 receives a pilot signal (known by radio base station 100 and the UE 200) transmitted through a pilot channel (CPICH: Common Pilot Channel) (see reference number A5). In accordance with the received pilot signal, each UE 200 measures a downlink propagation environment, that is, reception quality (SIR: Signal-to-Interference Ratio), calculates a CQI (Channel Quality Indicator) representing downlink reception quality based on the measured SIR, and notifies the radio base station 100 of the calculated CQI through HS-DPCCH (High Speed Dedicated Physical Control Channel) (see solid arrow A3).
Considering the downlink reception quality information (CQI) notified by UEs 200, the radio base station 100 schedules preferential selection of a predetermined number of UEs in a good propagation environment. If a certain UE 200 is selected by the scheduling, the radio base station 100 transmits scheduling information (including the modulation method, the transmission amount, and others) to the UE 200 through HS-SCCH (High Speed Shared Control Channel) (see broken arrow A4). The UE 200 determines the functions of the UE 200 itself with reference to the received scheduling information.
After that, the radio base station 100 transmits user information to the UE 200 through a radio channel called HS-PDSCH (High Speed Physical Downlink Shared Control Channel) (see broken arrow A4). The HS-PDSCH for transmission of user information is commonly used by all UEs 200, and a single time slot generated by time division is shared by one or more UEs 200 to realize downlink access of 14.4 Mbps at maximum.
FIG. 4 shows the concept of HSUPA communication. As shown in FIG. 4, uplink transmission from the UE 200 to the radio base station 100 is performed by communication HSUPA.
In other words, the UE 200 sends the radio base station 100 SI (Scheduling Information) as a request for uplink data transmission (see solid arrow A6).
The radio base station 100 collects a number of pieces of SI sent from UEs 200, schedules transmission timings for uplink transmission of UEs 200 based on communication quality of each UE 200, data priority and other factors, and finally transmits “Grant” indicating uplink transmission permission to UEs 200 (see broken arrow A7). “Grant” is classified into two types of “absolute Grant” and “relative Grant”: “absolute Grant” is used to notify an uplink transmission rate and others at regular intervals and “relative Grant” is used to notify update information of contents notified in the “absolute Grant”.
UEs 200 transmit user information to the radio base station 100 through channels called E-DCH (Enhanced Dedicated Channel), dedicated one to each UE 200, in order of being permitted transmission in the form of receipt of “Grant” from the radio base station 100 (see solid arrow A8) whereby high-speed uplink access is made possible. The transmission rate through an E-DCH is being examined to be approximately 2-5 Mpbs.
HSDPA adopts an adaptive coding and modulation method, and is characterized by, for example, switching a modulation method between QPSK modulation and 16 QAM modulation according to a radio environment between the radio base station 100 and the UE 200. In order to realize communication in the adaptive coding modulation method, the UE 200 defines the CQI to report the reception environment to the radio base station 100 and a CQI table defines formats different in transmission power which formats vary with the value of the CQI in the range of, for example, from 1 through 30.
Then the UE 200 measures the reception environment, and if it is assumed that the UE 200 receives data through the HS-PDSCH within 3 slots from the immediately before the slot of transmission of CQI under the measured environment, reports a CQI which is the maximum among CQIs not exceeding the BLER (Block Error Rate)=0.1 of the HS-PDSCH or which is less than the maximum CQI to the radio base station 100.
In the meanwhile, in HSUPA, the radio base station 100 monitors the total uplink interference amount (reception power) of controlling UEs 200, and as a result of comparison between the reception power and a threshold, indicates the absolute value of transmission rate using E-AGCH (a command indicating the absolute value of the maximum rate) or indicates increase, holding, or decrease in the transmission power using E-RGCH (a command indicating a relative value of the maximum rate). The UE 200 if having uplink transmission data transmits SI (a scheduling request) to the radio base station 100.
SI indicates information concerning transmission data that the UE 200 is to transmit which information is exemplified by “highest priority logical channel ID”, “total data amount of all the logical channel”, “total data amount of highest priority logical channel”, and “a transmission power that a UE 200 can transmit” that are mapped on the SI.
FIG. 6 shows frame formats of E-DPDCH (Enhanced-Dedicated Physical Control Channel) and the E-DPDCH (Enhanced-Dedicated Physical Data Channel) that are dedicated to the E-DCH. As shown in FIG. 6, the E-DCH is formed by two channels of: (1) E-DPCCH for transmission of control information and (2) E-DPDCH for transmission of data. The E-DPCCH maps control information (uplink control data) for uplink data such as an E-TFCI (E-DCH Transport Format Combination Indicator), an RSN (Retransmission Sequence Number) and a Happy bit, thereover. Here, the E-TFCI is information indicating that an uplink radio frame to be transmitted along with the uplink data is mapped over a transport channel, and the RSN is information indicating the number of uplink HARQs (Hybrid Automatic Repeat Requests) transmitted. Further, the Happy bit is information indicating whether or not the UE 200 requires additional resource (transmission power resource).
Following Patent Reference 1 discloses reduction in a bit number of scheduling information improves the efficiency of communication. Following Non-Patent Reference 1 serves as an exemplary material about a physical channel and a transport channel for W-CDMA including HSUPA. Following Non-Patent References 2 and 3 serve as exemplary materials about a physical layer of HSUPA.    [Patent Reference 1] Japanese Patent Application Laid-Open (KOKAI) No. 2005-6293    [Non-Patent Reference 1] 3GPP TS 25.211 Release 7 (V7.0.0) (2006-03)    [Non-Patent Reference 2] 3GPP TS 25.212 Release 7 (V7.2.0) (2006-09)    [Non-Patent Reference 3] 3GPP TR 25.808 Release 6 (V6.0.0) (2005-03)
In succession, FIG. 5 shows elements of the UE 200 having a function for transmitting the SI (scheduling request) UE 200 shown in FIG. 5 includes, for example, a receiver 201, an HS-SCCH demodulator 202, an HS-SCCH decoder 203, an HS-PDSCH demodulator 204, a CQI reporting value calculator 205, an HS-PDSCH decoder 206, an HS-PDSCH CRC operator 207, a downlink L2 (Layer 2) data processor 208, a downlink reception timing monitoring and uplink transmission timing managing section 209, a CQI/ACK/NACK scheduler 210, an HS-DPCCH encoder 211, an HS-DPCCH modulator 212, an uplink L2 (Layer 2) data processor 213, an E-TFCI/RSN/Happy-bit scheduler 214, an E-DPCCH encoder 215, an E-DPCCH modulator 216, an uplink scheduling request processor 217, an E-DPDCH encoder 218, an E-DPDCH modulator 219, and a transmitter 220.
In the UE 200 having the above-described elements and parts, a signal received at a reception antenna (not shown) is inputted into the receiver 201, where a path detection and an inverse diffusion process are performed to separate the CPICH, the HS-SCCH and the HS-PDSCH from one another.
The CPICH (a pilot signal) obtained by the separation is inputted into the CQI reporting value calculator 205 to be used for calculating a CQI reporting value. In other words, a downlink reception SIR is measured in accordance with the received pilot signal and a downlink CQI is calculated considering the result of the measurement. The calculated CQI is subjected to an encoding process, a modulation process, and a radio transmission process while passing the CQI/ACK/NACK scheduler (hereinafter also simply called “scheduler”) 210, the HS-DPCCH encoder 211, the HS-DPCCH modulator 212, and the transmitter 220, and is then transmitted to the radio base station 100 through the HS-DPCCH. The obtained pilot signal is also used to calculate channel estimation values of the HS-SCCH and the HS-PDSCH.
The HS-SCCH separated in the receiver 201 undergoes a channel compensation using the channel estimation value obtained on the basis of the received pilot signal and then a demodulation in the HS-SCCH demodulator 202, and is decoded in the HS-SCCH decoder 203. The result of the decoding includes information (e.g., an encoding method, an encoding ratio) required to decode the HS-PDSCH and is therefore inputted into the HS-PDSCH demodulator 206.
The HS-PDSCH separated by receiver 201, which has been subjected to a channel compensation using the channel estimation value and demodulation in HS-PDSCH demodulator 204, is decoded in HS-PDSCH decoder 206 using the result of decoding from HS-SCCH decoder 203 and is used for a CRC operation in HS-PDSCH CRC operator 207 for error check.
The decoded data that has been judged to have no error (CRC operation result of which is OK) is regarded as received data of the downlink layer 2 and is therefore inputted into the downlink L2 data processor 208, where a predetermined data processing is performed on the decoded data.
The result of the CRC operation is inputted into the scheduler 210, which schedules, along with the CQI reporting value, reception result information of ACK (Acknowledgment) or NACK (Negative Acknowledgment) respectively corresponding to the CRC-operation result being OK or NG. The CRC-operation result is then subjected to an encoding process, a modulating process and a radio transmission process while passing the HS-DPCCH encoder 211, the HS-DPCCH modulator 212, and the transmitter 220, and is finally notified to the radio base station 100 through the HS-DPCCH.
In the meanwhile, concerning the uplink, if data that is to be transmitted to the radio base station 100 is present at the uplink L2 data processor 213, the E-TFCI/RSN/Happy bit scheduler 214 generates uplink control data, which undergoes an encoding process, a modulation process and a radio transmission process while passing the E-DPCCH encoder 215, the E-DPCCH modulator 216, and the transmitter 220 and is transmitted to the radio base station 100 through the E-DPCCH. Further, the uplink scheduling request processor 217 generates uplink SI, on which an encoding process and a modulating process and a radio transmission process are performed in the E-DPDCH encoder 218, the E-DPDCH modulator 219, and the transmitter 220 and which is consequently transmitted to the radio base station 100 through the E-DPDCH.
The transmission timings of the HS-DPCCH, the E-DPCCH, and the E-DPDCH from the transmitter 220 are managed in accordance with a transmission timing signal from the downlink reception timing monitoring and uplink transmission timing managing section 209 (hereinafter simply called “timing management section”). In other words, the timing management section 209 manages transmission timings (transmission slots) of the HS-DPCCH, the E-DPCCH, and the E-DPDCH with reference to reception timings (frame timings) specified by a frame synchronization process performed in the receiver 201, and controls the transmission timing of the transmitter 220 to be a predetermined timing in accordance with the transmission timing in question.
FIG. 7 is a diagram illustrating a digit of the Happy bit. As shown in FIG. 7, the Happy bit transmitted through the E-DPCCH indicates either the “Happy state” (Happy bit of “1”) in which the UE 200 does not require an additional resource or the “Unhappy state” (Happy bit of “0”) in which the UE 200 requires an additional resource. If all the three following conditions are satisfied, the “Not happy (Unhappy) state” representing a requirement for an additional resource is notified to the radio base station 100.
(1) UE is transmitting schedule data of the maximum amount permitted under the current SI.
(2) UE can use sufficient power that allows transmission at a higher data rate.
(3) A transmission delay of the uplink data is a predetermined value or more, so that transmission of the uplink data accumulated in the buffer of the UE cannot be completed within the predetermined time limit.
Accordingly, for example, if the communication environment (communication quality) between the radio base station 100 and the UE 200 does not satisfy a certain level while the UE 200 nevertheless transmits uplink data to the radio base station through the E-DPDCH at the maximum transmission power, a lack of an uplink transmission rate may fail in completion of transmitting of all uplink data. But the above case dissatisfies the condition (2) that “UE can use sufficient power that allows transmission at a higher data rate.” As a result, the UE 200 notifies the radio base station 100 of the “Happy state” indicating not requiring the additional resource, and cannot request the radio base station 100 for allocation of the additional resource. That may cause a problem that transmission of uplink data cannot be normally completed.